Liquid crystal display devices are provided to the ceiling of a cabin of an airplane or the like, are horizontally stored within the ceiling, and are opened to a substantially perpendicularly deployed position when necessary. When the liquid crystal display device is opened, rotational movement output via a motor and reducer is converted to circular movement for turning the liquid crystal display to an deployed position via a link mechanism. A spiral spring is connected to an input shaft or output shaft of the reducer, and is designed to be wound up in association with the opening action of the liquid crystal display device. When the liquid crystal display is to be stored, the motor and the reducer are separated by an electromagnetic clutch, and the returning force of the wound-up spiral spring returns the liquid crystal display device to the stored position. The rotational force of the motor is not relied upon for the closing action because the liquid crystal display device must reliably be returned to a safe stored position without relying on electrical power even in an emergency.
In this instance, the liquid crystal display device 1 is in a substantially flat orientation when in a stored position 1A, and is in a substantially perpendicular orientation when in an opened position 1B, as shown in FIG. 5(b). Therefore, a torque T(1) based on the weight that turns the liquid crystal display device 1 in the opening direction is at a maximum in a closed state, is reduced as the display device is turned toward the deployed position 1B, and is at a minimum when the device is in the perpendicular orientation, as shown in FIG. 5(a). In contrast, the spiral spring will have the least number of coils (state of the initial number of coils) when the liquid crystal display device 1 is closed; therefore, the returning force T(18) of the spiral spring will be at a minimum. The number of coils will be at a maximum when the liquid crystal display device 1 reaches the deployed position 1B; therefore, the returning force T(18) will also be at a maximum. The returning force T(18) in the state of the initial number of coils must exceed the torque T(1) in the opening direction created by the weight of the liquid crystal display device 1 when in a closed state in order for the liquid crystal display device 1 to be returned to the stored position 1A by the spiral spring.
Configuring the returning force of the spiral spring in this manner poses a hazard in that a return torque T(1+18) that will be at maximum in the deployed position and decreases toward the stored position, will act on the device, so that the returning torque in the deployed position will become extremely high, and the liquid crystal display device 1 will slam shut.
A demand has arisen for a braking mechanism to be affixed to a retracting device of the liquid crystal display device 1 for applying a brake so that the liquid crystal display device will close at suitable speed. Braking mechanisms able to be used include hydraulic dampers, electromagnetic brakes, and gear dampers in which the braking force increases in proportion to the speed. However, problems are presented in that gear dampers comprise a plurality of gears, are configured so that frictional force increases with centrifugal force, involve a complex mechanism, and have poor reliability. Problems are also presented in that hydraulic dampers must be of a large size in order to maintain a prescribed braking force and are not suitable for being incorporated in retracting devices for liquid crystal display devices and the like. Problems further arise in that an electromagnetic brake or other electrical brake will not function during a power failure.